Sharpstar 2.5" universal field flattener for APO refractors

Sharpstar 2.5" universal field flattener for APO refractors

Sharpstar 2.5" universal field flattener for refractor, suitable for sensor size up to full-frame format and much more (corrected image circle up to 55 mm). This field flattener is deisgned to correct the image of apochromatic refractors from 500 to 1000 mm just by varying the working distance (from 87 to 106 mm). Fully Multy-coating on each lens surface and blackened interior for reflection suppression. Includes M48 adapter with distance already calculated for 700 mm focal length triplet refractors such as the Sharpstar AL-107PH.

A polyvalent universal field flattener

This field flattener can be adapted to any apo refractors with focuser of at least 2.5" and first directly any focuser that shows a Zeiss standard thread (female M68x1) or an M63x1 female thread, such as in many sharpstar refractors. The refractor must have at least 145 mm of back focal length from M68 thread (150 mm from M63 thread) in order to reach focus with this field flattener.

CCD side there is a male M69x1 thread, but the box includes also a M48 adapter with distance already calculated for 700 mm focal length triplet refractors such as the Sharpstar AL-107PH.

Metal back distance

The Sharpstar 2.5" field flattener is optically compatible with lot of refractors actually available in the market, you will just have to set the proper working distance in order to achieve optimal correction.

Following a list of the suggested metal back distances:

• for focal lengths up to 500 mm suggested distance is 106 mm
• for focal lenghts from 510 to 600 mm suggested distance is 101 mm
• for focal lenghts from 610 to 700 mm suggested distance is 96 mm
• for focal lenghts from 710 to 800 mm suggested distance is 91 mm
• for focal lenghts from 810 to 950 mm suggested distance is 88 mm
• for focal lengths over 1000 mm suggested distance is 87 mm

Intermediate distances can be tried in order to reach optimal performances. We remind that you have to consider the optical backfocus of your system, including - for instance - also any optical filters used in the imaging train (any optical filter adds 1/3 of its physical thickness to the backfocus). If you have any doubts you are invited to contact us, we can help you to define the proper distance for your imagin train.

Adapters available

There are dozen of adapters commercfially available that can help you to fit your CCD or CMOS camera to the Sharpstar 2.5" field flattener. We can also build custom high-precision adapters. You are invited to contact us for help.